Semiconductor fabrication process chambers commonly employ plasmas to enhance the performance of various processes for fabricating semiconductor devices on silicon wafers or other workpieces. Such processes include sputter etching, plasma-enhanced chemical etching, plasma-enhanced chemical vapor deposition, and ionized sputter deposition. The high energy level of reagents in the plasma generally increases the rate of the fabrication process, and often reduces the temperature at which the semiconductor workpiece must be maintained to perform the process.
Magnetically-enhanced plasma chambers employ magnetic fields to increase the density of charged particles in the plasma, thereby further increasing the rate of the plasma-enhanced fabrication process. Increasing the process rate is highly advantageous because the cost of fabricating semiconductor devices is directly proportional to the time required for fabrication.
Despite this advantage, many plasma chambers in commercial use do not employ magnetic enhancement, because magnetic enhancement has been found to increase the likelihood of damaging the semiconductor devices on the wafer. (See Fang & McVittie, "Charging damage to gate oxides in an O.sub.2 magnetron plasma", J. Appl. Phys., vol. 72, no. 10, pp. 4865-4872, Nov. 15, 1992; and Fang & McVittie, "The role of `antenna` structure on thin oxide damage from plasma induced wafer charging", Mat. Res. Soc. Symp. Proc., vol. 265, pp. 231-236, 1992.) Therefore, a need exists for a magnetically-enhanced plasma chamber that affords the benefits of conventional magnetic enhancement but with a reduced risk of semiconductor device damage.